TESORO GOLDEN SABRE

[Pompey]

DD27/TX 5,89mH;20,7ohms freq.13,9
RX 6,38mH;21,5ohms freq.13,4

Hi ,Ultimate Haze.My last Tx coil is 5,9mH,and workin frequency is 14,53khz.I use 0,27mm. It seems your LC meter doesn`t measure exact inductances.I use my LC-meter in 200mH range to measure.When I put it on 20mH it gives mi incorrect inductance -raises up to 2mH.I measure frequency with 3 different meters - one multicet,LC-meter(multicet) and with PC-osciloscope -sound card.LC-meter gives 350 hz less frequency than the others.The pc and the other multicet show the same.

[Ultimate_Haze]

DD27/TX 5,89mH;20,7ohms freq.13,9
RX 6,38mH;21,5ohms freq.13,4

[Pompey]

" ...Is there a possibility that when even the nulling seems fine , the sensitivity is poor ?..."

"Nulling seems fine" but you must understand that coils nulled well on one frequency are not nulled well on another (different) frequency. Residual voltage rised if frequency changed.

I think Qiaozhi already gave here good hint. Keep RX coil resonance within +1.8 - +2kHz than TX coil.
And use pp caps.

BTW thank You very much on your effort making those clips!
Best Regards!

************************************************** *
I think if you are able to adjust geb pot -rejecting ferrite somewhere in the middle off resonanse is OK -about 1,8-2,2khz. By adding,removing capacities to 15nf and playing with geb pot you can find the exact place where the ferrite is rejected not at any of ends of the POT,but somewhere in the middle.I think this happens when you achieve correct off resonance.But at the ferrite rejection has influence and this 220nf capacitor from pin 7 of LF353.By changing it you also may achieve ferrite to be rejected at correct point of geb pot.So what the experts will say?

[ivconic]

?

[gurdal]

Hi ivonic, if damage is plastic box

[ivconic]

Hello,
So it might be multimeter that is wrong.I will try with oscilloscope.What you recommend?Directly from RX or LF353 pin7?
It still might be bad component no matter that I remove most and test those.
Tonight I will remove all.Just to make shore.

No it is not wrong. Simply it is not designed to measure such values. Although...i also have conventional multimeter (brand new, bought it 3-4 months ago) and i can measure 4mV...7mV...etc.
Well...there are 2 methods suggested. Both are ok. My method is directly from RX coil (no caps, no resistors..).
...
But seems you missed the point. Check how much is your RX coil off resonance from TX.

Connect TX coil to TGSL TX out and measure frequency on 2N2907 collector.
Than connect RX coil to TX out and measure frequency on 2N2907 collector.
Than let me know here...

[Ultimate_Haze]

Hello,
So it might be multimeter that is wrong.I will try with oscilloscope.What you recommend?Directly from RX or LF353 pin7?
It still might be bad component no matter that I remove most and test those.
Tonight I will remove all.Just to make shore.

[ivconic]

For a series resonant circuit the reactances (L and C) will create a very low impedance, whereas for a parallel circuit the reactances result in a very high impedance.

The TGSL uses an opamp for the RX pre-amp with a high impedance input and is configured as a voltage amplifier. Therefore I would not expect a series resonant circuit to function correctly in this configuration.

Give it a try and let us know the result.

I already tested yesterday on my diy Eldorado (i don't have TGSL right now).
An you are right, not good.
It will need more changes to make it to work descent. I am not planing to do that, i just experimented a bit to see the differences in practice...

[ivconic]

"...All have too high residual voltages.Around 1mV..."


So if you have 1mV residual voltage....hmmm....than your coil is "undernulled" or maybe you reached situaton where your multimeter cannot measure accurately. Generally, conventional multimeters are not best tools for measuring residual voltage. Good as something to start with, but not accurate. Scope is only solution.
Chasing less possible voltage on your multimeter you "undernulled" your coils and choked it, that's why it is not so good.

[Qiaozhi]

Qiaozhi and others;

i was thinking to experiment with serial LC at RX input? To make it more "wide band". What do you think about that?
BTW i always asked myself why at some designes we can see serial and at some parallel tuned coils? What are differences? (generally i think i understand the differences but would like to know details)

For a series resonant circuit the reactances (L and C) will create a very low impedance, whereas for a parallel circuit the reactances result in a very high impedance.

The TGSL uses an opamp for the RX pre-amp with a high impedance input and is configured as a voltage amplifier. Therefore I would not expect a series resonant circuit to function correctly in this configuration.

Give it a try and let us know the result.

[ivconic]

Hello,
I have almost same troubles with my last TGSL1265.
Still cant find whats wrong.I have over 12 different coils.Various sizes some are 22 /best I can reach is 20sm for 1e coin/some 27.Different L,including 6 and 6,5.But at this specific device no one from those give me 30-31sm on one euro coin.
Strangest thing is that I need 5,50mH for TX so I can read 14,6kHz.With 6mH its around 14kHz.Have check all caps several times.All ok.Also change different types capacitators at vital points.Have play with C9 from 100p to 68pf,40pf.
The coil cable is 4 cores with common shield like in picture.
Have add tresh. pot-no change.So I restore like it was.
So now no idea what else can I try.
I guess that will have to make another device.But because I have spend so much time on this one,curies what I did wrong?
Oh one more thing.On all coils its impossible to null to 0.07mV.All have too high residual voltages.Around 1mV.And no matter what I try the just refuse to tune better.Maybe too much noise inside?Wireless ,satTV ,etc.?

Ehhh! It was in the past when i had some strange multimeter and i got such funny measurements! I think i already corrected those and posted somewhere that residual voltage at good nulled coils is in range 4mV-7mV...athough it can work very good at up to 15mV too. (i had similar coils)
....
About frequency...you do not need to "chase" exact frequency at all. Keep it between 13.5 and 14.5 kHz and don't worry.
.....
What's than wrong there? Some bad component...or some bad spot in signal paths, nothing else.
Read my todays posts about resonance. Check at your coils (with presented caps) that.

[Ultimate_Haze]

Hello,
I have almost same troubles with my last TGSL1265.
Still cant find whats wrong.I have over 12 different coils.Various sizes some are 22 /best I can reach is 20sm for 1e coin/some 27.Different L,including 6 and 6,5.But at this specific device no one from those give me 30-31sm on one euro coin.
Strangest thing is that I need 5,50mH for TX so I can read 14,6kHz.With 6mH its around 14kHz.Have check all caps several times.All ok.Also change different types capacitators at vital points.Have play with C9 from 100p to 68pf,40pf.
The coil cable is 4 cores with common shield like in picture.
Have add tresh. pot-no change.So I restore like it was.
So now no idea what else can I try.
I guess that will have to make another device.But because I have spend so much time on this one,curies what I did wrong?
Oh one more thing.On all coils its impossible to null to 0.07mV.All have too high residual voltages.Around 1mV.And no matter what I try the just refuse to tune better.Maybe too much noise inside?Wireless ,satTV ,etc.?

[ivconic]

"...Keep RX coil resonance within +1.8 - +2kHz than TX coil...."

I just wanted to check this on datas from original Tesoro coils that are posted somewhere on Geotech forums in the past:

Brown 8" = 5.59mH(22nF) - 6.23mH(15nF) .....i got 2.11kHz off resonance,
White 8" = 5.68mH(22nF) - 6.36mH(15nF) .....i got 1.89kHz off resonance,
White 4" = 5.62mH(22nF) - 6.13mH(15nF) .....i got 2.29kHz off resonance...

So...i was pretty close! From 1.89 to 2.29 !

[ivconic]

Another thing;
am i wrong or i see TX amplitude there barely over 10vpp ?
That could be the cause of poor depths.
Usually amplitude is 15-16vpp at TGS/TGSL...

[ivconic]

Qiaozhi and others;

i was thinking to experiment with serial LC at RX input? To make it more "wide band". What do you think about that?
BTW i always asked myself why at some designes we can see serial and at some parallel tuned coils? What are differences? (generally i think i understand the differences but would like to know details)